It is possible that lenticular proteolytic enzymes play a role in the transition of soluble proteins into the insoluble state, the formation of aggregates, damage to certain membranes, loss of protein in aging and cataractous lenses and denaturation resulting in opacification of certain areas within the lens or the entire lens structure (Hahn, 1976). Despite these correlations, information on the lens proteases in scanty. Studies have correlated Leucine Aminopeptidase (LAP) activity with cataractogenesis with conflicting conclusions. We began to study LAP because it has been associated with cataractogenesis and because it is representative of a class of enzymes, the aminopeptidases, which unlike the endo and carboxypeptidases, has not had its tertiary structure and mechanism of action determined. Our recent kinetic data indicate that the confusion regarding the role of LAP in cataractogenesis may be due to the unspecific substrates used in assays. This research has two major objectives. The first set of goals is a continuation of my previous studies on the enzyme which were done with Dr. F.H. Carpenter at the University of California, Berkely. I will pursue the three-dimensional structure in collaboration with Dr. Alex Rich at MIT, attempt to determine the amino acids at the active site using affinity labels, continue probing the specificity and mechanism of action of LAP using kinetic tests of substrate analogs and nuclear magnetic resonance. The NMR work will be done with the help of T. James of the University of California, San Francisco. Our second objective will involve use of very specific activity assays and immunological techniques to see if correlations exist between LAP, in either its active or inactive form, and cataractogenesis. Using immunofluorescence we hope to determine if there is a function-location relationship for LAP in bovine, hog, rabbit normal and diseased lenses and in human cataractous lens tissue.